1. Field of the Invention
The present invention relates to a control element for an electric control device having a freely programmable symbolic system, whereby the symbols are projected into a side of the control element, which is facing away from the user, by a controllable display unit and an illuminating device arranged in front thereof, or by a controllable display unit and optics, or by a controllable display unit and a light guide, and the symbols are made visible by a transmissive layer on the side of the control element that faces the user. Furthermore, the invention is directed to a method for generating freely programmable symbols on the control element of an electric control device, whereby symbols are projected into the interior face of the control element by an illuminating device and a controllable display unit, or by a controllable display unit and optics, or by a controllable display unit and a light guide, and whereby the generated symbols are transmitted via a transmissive layer on and in the control element to a surface facing the user so that the user can recognize a symbol corresponding to the function of the control element.
Although the control element can be used in any kind of control device, for example, in control devices for motor vehicles, input devices for cash registers etc., the present invention and its objectives are described with reference to a control device in a motor vehicle.
2. Description of the Background Art
To control the multiple functions in a motor vehicle, control devices are most frequently installed in the center console or the dashboard. These control devices are then provided with control elements, some of which can control various functions. To avoid having to provide a multi-function control element, that is, a control element, to which various functions are allocated, with a plurality of symbols, it is known from the published patent application DE 103 42 142, which is assigned to the Applicant of the present invention, to provide control elements with freely programmable symbols. An image is hereby generated in a controllable display unit, for example, an LCD display unit, which is projected onto an image plane in the control element so that it becomes visible to an observer of the control element from the front. By using a freely programmable display unit, any desired symbol can thereby be generated on the surface of the control element.
A plurality of corresponding methods and devices are described in the publication (DE 103 42 142), which make it possible to project an image of the symbols generated in the display unit as positive or negative. In a first embodiment, a control element is described, in which a display unit is impacted with parallel light by an illuminating device, which is arranged behind an optical system, for example, a lens. Depending on the generated symbols, there are transmissive or absorbing areas in the display unit so that the display unit serves as a transmission filter. The light rays penetrating the display unit form the image of the symbols on the inner surface of the control element. The control element itself is made of a translucent material so that the generated symbols become visible on the side of the control element that faces the operator. In order to control the configuration and the behavior of the ray in the control element, and to be able to provide an exact image on the control element, various embodiments comprising illuminating units, display units, optics and fiber materials are described in the publication, whereby the dynamic movements of the control element during actuation are also taken into consideration. The described system makes it thus possible to display to the user different symbols on the surface of the control element, depending on the function designated to the control element.
DE 100 08 670 C2, which corresponds to U.S. Pat. No. 6,198,061, also discloses a device for displaying various symbols on a control element. An image guide, which guides the information presented on the screen of the indicator unit close to a switch cap, is provided between the indicator unit and the switch cap. With the conventional switch arrangement, if a plurality of functions is assigned to the switch cap, the information displayed on the screen of the indicator unit is altered in correspondence with a function change so that the symbol of the switch cap changes accordingly to allow a multiple display on one single switch cap.